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A still is an apparatus used to distill miscible or immiscible (eg. steam distillation) liquid mixtures by heating to selectively boil and then cooling to condense the vapor. Stills have been used to produce perfume and medicine, Water for Injection (WFI) for pharmaceutical use, generally to separate and purify different chemicals, and most famously, to produce distilled beverages containing ethyl alcohol.
Additional recommended knowledge
Main article: distilled beverage
Since ethyl alcohol boils at a lower temperature than water, a common application of the process of distillation is to produce strong alcoholic drinks. Usually a still used for this purpose is made of copper, since it removes sulfur-based compounds from the alcohol that would make it unpleasant to drink. Modern stills are made of stainless steel with copper innards (piping, for example, will be lagged with copper along with copper plate inlays along still walls). Using this combination of metals is much cheaper as it prevents erosion of the entire vessel and lowers copper levels in the waste product (which in large distilleries is processed to become animal feed). All copper stills will require repairs about every 8 years because of copper erosion from the compounds it is designed to remove; this erosion is therefore unavoidable. The alcohol industry was the first to use anything close to a modern distillation apparatus and led the way in developing what is now a large part of the chemical industry.
The simplest standard distillation apparatus is commonly known as a pot still, consisting of a single heated chamber and a vessel to collect purified alcohol. A pot still incorporates only one condensation, whereas other types of distillation equipment have multiple stages which result in higher purification of the more volatile component (alcohol). Pot still distillation gives an incomplete separation, but this can be desirable for the flavor of some distilled beverages.
If a purer distillate is desired, a reflux still is the most common solution. Reflux stills incorporate a fractionating column, commonly created by filling copper vessels with glass beads to maximize available surface area. As alcohol boils, condenses, and reboils through the column, the effective number of distillations greatly increases. Vodka and rum are both distilled by this method, then diluted to concentrations appropriate for human consumption.
Alcoholic products from home distillaries is common throughout the world, but is sometimes in violation of local statutes. The product of illegal stills in the United States is commonly referred to as moonshine.
Categories: Distillation | Separation processes
|This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Still". A list of authors is available in Wikipedia.|